1. Field of the Invention
The present invention relates to a stocker for accommodating, storing or transporting articles. More particularly, the present invention relates to a stocker for accommodating, storing or transporting, for a long time or temporarily, articles (materials, semi-fabricated products, or finished products) such as liquid crystal display substrates or silicon wafers for forming semiconductor chips, or valuable articles in clean, contamination-free conditions.
2. Description of Prior Art
Prior art will be described below with regard to the process for producing liquid crystal displays.
The production of a liquid crystal display is carried out through a large number of steps. For example, the process for forming patterns on glass substrates formed with transparent electrically conductive films includes various steps, i.e., washing, coating of a photoresist, exposure, etching, drying, etc. The subsequent assembly process includes steps of formation of alignment film, firing, rubbing, printing of a sealing compound, bonding, and injection of a liquid crystal material.
Thus, the liquid crystal display producing process comprises a large number of steps. In addition, liquid crystal displays are increasing more and more in size and are showing an increasing tendency to become higher in precision. Consequently, patterns to be formed are demanded to further increase in the degree of fineness and precision. Accordingly, there is a rapidly increasing need for reducing defects generated in each individual step of the manufacturing process.
Effective ways of reducing defects include (1) to keep each step clean continuously, and (2) to carry out effective washing. It is a particularly effective way to keep each step clean (at a high degree of cleanliness) continuously.
Meantime, during the manufacturing process, liquid crystal display substrates, semi-fabricated products, etc. are temporarily accommodated, stored or transported in accordance with the kind of process carried out at each step.
For the accommodation or storage, it is general practice to use (1) equipment having an opening in a part thereof, e.g., a clean bench or a clean booth, or (2) a stocker having a closed structure isolated from the external environment, e.g., one which is equipped with an HEPA (High Efficiency Particulate Air Filter) or ULPA (Ultra Low Penetration Air Filter) filter so as to provide a dust removing function, or another which is provided with a dust removing function by a vacuum. For the transportation, a storage carrier with a closed structure which is provided with a dust removing function by a vacuum is generally used.
However, all of the above-described systems are inferior in performance, so that articles contained therein may be contaminated during accommodation, storage or transportation. For example, in the system that employs an ULPA filter, air is previously passed through the ULPA filter to purify the air, and the purified air is returned to the stocker so as to purge the inside thereof, thereby cleaning the inside of the stocker. With this system, since the air is forcedly circulated through the stocker, fine particles are generated therein. Accordingly, the system is limited in ability to realize ultra clean conditions. In addition, since fine particles in the stocker are forcedly circulated, they may adhere to valuable articles in the stocker, thus giving rise to a problem.
Further, the prior art systems that employ a vacuum for dust removing purposes are difficult to handle.
Thus, the conventional systems have practical problems to be solved.